fix: exempt admins from default user group limits

crates/aether-data/migrations/postgres/20260509120000_add_user_groups.sql

@@ -98,4 +98,5 @@ INSERT INTO public.user_group_members (group_id, user_id)
 SELECT '00000000-0000-0000-0000-000000000001', id
 FROM public.users
 WHERE is_deleted IS FALSE
+  AND LOWER(role) <> 'admin'
 ON CONFLICT (group_id, user_id) DO NOTHING;

crates/aether-data/migrations/postgres/20260511120000_exclude_admins_from_default_user_group.sql

@@ -0,0 +1,12 @@
+DELETE FROM public.user_group_members AS member
+USING public.users AS users
+WHERE member.user_id = users.id
+  AND LOWER(users.role) = 'admin'
+  AND (
+    member.group_id = '00000000-0000-0000-0000-000000000001'
+    OR member.group_id IN (
+      SELECT value #>> '{}'
+      FROM public.system_configs
+      WHERE key = 'default_user_group_id'
+    )
+  );